The present invention relates to a vibration damping system used to absorb and damp the vibrations due to earthquakes of pipelines, pumps, or other machinery and structures, the vibrations due to flowing fluids and the vibrations of engines and turbines.
Vibration damping systems used in nuclear power plants or chemical plants must provide not only a function of permitting thermal displacement of an equipment to be vibration-damped so as to protect it but also a function of suppressing sudden vibrations such as earthquakes.
Conventional vibration damping systems having the above-described two functions are oil snubbers, oil dampers and mechanical snubbers.
Oil snubbers and oil dampers are devices utilizing hydraulic pressure in which, as shown in FIG. 1, a cylinder 2 is securely mounted on a stationary support 1 and a piston 3 is inserted into the cylinder 2 which is filled with an oil. The right and left cylinder spaces of the cylinder 2 divided by the piston 3 are intercommunicated through a pipe 4 with a restriction 5 and poppets 6 and 7 disposed on both sides of the restriction 5. A fee end 8a of the piston rod 8 is connected to an equipment to be vibration-damped (that is, various devices, equipment, strustures and pipelines whose vibrations must be suppressed and damped). Springs 9 and 10 are disposed to normally urge the poppets 6 and 7, respectively, away from the restriction 5. When the hydraulic pressure in the cylinder 2 is decreased (that is, when the movement of the piston 8 is slowed down), the poppets 6 and 7 are urged away from the restriction 5 so that the resistance of the fluid passage can be decreased. When the equipment to be vibration-damped vibrates and the piston 3 is caused to move, the poppet 6 or 7 closes the restriction 5 so that the displacement of the piston 3 is suppressed to suppress vibrations. However, the device or system described above has the disadvantages: (1) that inspection is needed because of the leakage of working oil during use: (2) that the device is heavy in weight: (3) that the device is complex in construction and therefore very expensive in cost and constant maintenance works are needed because of very frequently break-downs: and (4) that the vibration damping device cannot support itself.
Mechanical snubbers mechanically damp vibrations in which, as shown in FIG. 2, a ball nut 12 is securely attached to a load column 11 to which is connected an equipment to be vibration-damped, and is threadably engaged with a ball screw 13 so that reciprocal linear movement of the equipment to be vibration-damped is converted into rotary movement of the ball screw 13. A a disk spring 14 is securely attached to the end portion of the ball screw 13 and the time lag between the disk spring 14 and a flywheel 15 rotatably mounted is utilized to produce braking action due to the contact between a brake shoe 17 and a brake disk 18, thereby stopping the rotation of the ball screw 13. This device is further provided with balls 16. The above-described construction is substantially similar to that of a disk brake which is actuated in response to an acceleration so that no braking action is produced in response to the slow movement of the equipment to be vibration-damped and almost no resisting force is produced. The mechanical snubber of the type described has no problem of the leakage of working oil, but it still cannot solve the other disadvantages ((2)-(4) described above) of the oil snubbers.
The present invention was made to overcome the above and other problems encountered in the conventional vibration damping systems and has for its object to provide a vibration damping systems which can substantially overcome various defects due to the complicated construction of the conventional oil snubbers and mechanical snubbers; which can improve reliability in operation by eliminating the leakage of working oil, sticking (the phenomenon that the device cannot move) and other defects; which can substantially eliminate maintenance works; which can be made light in weight and compact in size so that the manufacturing costs can be reduced; and which is provided with a mechanism capable of positively absorbing the vibration energy.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings.